# pot 'biasing' for a joystick

#### CaliusOptimus

Joined Aug 14, 2005
59
i have an old usb joystick that i tore apart for use with my microcontroller, and ive tried a couple different things to solve the problem of the pots not reaching their extremes (being configured as a voltage divider [5v power], they were within about 1v min and 3v max). any software compensation reduced the resolution, so i tried using positive and negative voltage regulators (317's and 337's) to bias them, but they were somewhat unreliable and required a dual supply. im rather stumped on the subject. any ideas?

#### hgmjr

Joined Jan 28, 2005
9,027
Is the problem that the minimum and maximum voltages are mechanically limited to the values you stated?

hgmjr

#### bloguetronica

Joined Apr 27, 2007
1,521
Why don't you use resistors in series with the pot. For example:
Vcc - R1 - POT - R2 - Ground (must be in that order).
Remember: R1 = 2 x R2 = Rpot. Then you would get the required voltage in the cursor terminal of the pot.
Anyways, the 5V are regulated. You could simple use a voltage divider such as that without any problem.

#### CaliusOptimus

Joined Aug 14, 2005
59
hgmjr,

the pots for the x and y axis are able to travel about 300 degrees total, and the mechanical limits of the joystick only allow for them to travel 30-45 degrees in either direction. hence a range of about .75v-3v on the wiper. (i wasnt sure when i posted, so i checked). seeing as the pots aren't particularly 'linear', centered position is about 2v. i cant tell if they're just cheap or logarithmic.

cumesoftware,

if understand you correctly, doing that would further limit the voltage range, making my problem worse. lol im sorry if i wasnt clear in my original post.

#### hgmjr

Joined Jan 28, 2005
9,027
In the end, I think you are pretty much stuck with dealing with the joystick as it is. Since there are mechanical constraints on the physical movement of the joystick, most anything you do from an electrical perspective will degrade the resolution of the output.

That said, I don't see any reason to keep you from getting a useable output without making any changes at all. Just use the restricted range and you will realize the optimum resolution.

If the pots are non-linear then you may need to consider abandoning your hope of using it.

hgmjr